1. Field of the Invention
The present invention relates to a power supply circuit for producing a reference current with a prescribable temperature dependence, the circuit in which two current sinks are provided, which at their respective input take up a first input current or a second input current, and in which the current sinks at their respective output are connected to a node having a reference potential, the output of at least one current sink being connected via a resistor to the node having the reference potential.
2. Description of the Background Art
Power supply circuits are known and are used, for example, in integrated circuits to create internal voltage references with a prescribable or disappearing temperature dependence.
Two current sinks can be made hereby as MOS field-effect transistors, whereby drain currents of the field-effect transistors correspond to the input currents. The field-effect transistors, e.g., because of the different layout of the surface area of their respective gate electrodes are designed in such a way that at identical input or drain currents, different current densities and thereby also different gate-source voltages of the field-effect transistors result, whereby a voltage resulting from the difference of the different gate-source voltages, in addition to an area ratio of the respective gate electrodes, depends on the ambient temperature, among other factors. This temperature-dependent voltage is applied to the resistor that connects an output of a current sink, i.e., a source electrode of the corresponding field-effect transistor, to a node having a reference potential. In this way, the temperature dependence of the current flowing through the resistor can be set with use of the known temperature dependence of the aforementioned voltage and of a resistor with a prescribable temperature coefficient. This current is also designated as the reference current within the meaning of the present invention.
Another circuit that uses bipolar transistors as current sinks is cited, for example, in Tietze, U., Schenk, Ch.: Halbleiterschaltungstechnik (Semi-conductor Technology); 10th ed., Berlin, Springer 1993, FIG. 26.20 on page 900.
Moreover, a method for producing an output current with a prescribed temperature coefficient is known from DE 102 22 307 A1, which corresponds to U.S. Publication No. 2003214277, in which currents of two current sinks are added or subtracted from one another and wherein the currents and/or temperature coefficients of the current sinks are different from one another.
It turned out, however, that with these conventional devices, particularly in a realization of the power supply circuit in the form of an integrated circuit, not all possibly desired temperature dependences of the reference current flowing through the resistor can be set. With use of the conventional devices, no reliably operating power supply circuits could be realized, particularly for very small reference currents in the nanoampere range, especially for current strengths of about 20 nA to 50 nA.